having custom bolts made 1

[SceneryDriver]

Hi All,
Please forgive me if I don't supply all the details correctly - I'm a controls and electrical guy.

Here's my question:

The repertory theater company I work for uses several hundred of these fasteners (see pic link) a year; as our scenery for each show must go in and come out at least once a day, we need fasteners that can be put together and come apart hundreds of times a season. We currently use a fastener called an "improved stage screws." In the attached picture, the screw (with 3/8" Acme threads) threads into a steel insert driven into the stage deck. The insert has internal Acme threads and knife edge threads on the outside to bite into wood. The "flat head" screw also pictured is what we make from the stage screws; we cut the "bow" off, and cut slots for a flathead screwdriver with a cutoff wheel and grinder. Labor intensive and somewhat inelegant to say the least. Further, the quality of the steel used in both the male and female parts has declined in recent years and is close to butter-soft.

[

http://files.engineering.com/getfil...b8e8-4e72-9179-9120869c44c3&file=DSCN1940.JPG

]

In an ideal world, we'd like to have the "screws" made from a harder grade of steel (gr. 5 seems like a good compromise between toughness and tensile strength), and have the heads made with either hex or Torx drive. In a perfect world, we'd be able to source the inserts with a better grade of steel too, but that's negotiable. What would we be looking at to have a batch made in terms of minimums and production techniques? I've seen the "How It's Made" type shows demonstrate the cold-heading and roll threading processes, but I'd imagine the tooling would be very expensive at the quantities we're looking at - 500 or so at a time. We could possible purchase a larger batch depending on price breaks and minimums.

Who manufactures bolts by the batch, other than a machine shop? Is what I'm asking even reasonable and viable? I'm certainly open to other ideas as well.


Thanks for any assistance!



-SceneryDriver

 

[KENAT]

If you can find threaded rod of the appropriate thread, then machining a male hex onto it that you can then use with a socket set/wrench... should be pretty easy for any little machine shop and at a reasonable volume not crazy expensive.

Might be worth actually contacting a fastener supply store to see if they have any screws an appropriate size.

Posting guidelines faq731-376

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What is Engineering anyway: faq1088-1484​

 

[KENAT]

Sorry, if you need a head on the bolt you maybe able to put a nut on the thread, and bond, stake - or depending on grade - weld it in place.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[MikeHalloran]

Make a drawing and put it out for bids; there's no other way to get a real price.

You know those screws that hold the brackets into a PC? I had some custom units made once. I don't think there was a tooling charge, and the price was extremely low. The minimum order was something like 25,000 pieces. ... for ~$1200. That quantity of small screws won't fill an average bucket, so we got decades' worth with one order.

The other lesson: You may have to buy many more than you will ever need, so make the drawing complete and accurate.


Mike Halloran
Pembroke Pines, FL, USA

 

[SceneryDriver]

Mike,
Do you have a source for your custom screws? That company seems like a good starting place. I agree that we may end up needing to buy buckets worth. I guess we should consider it a long term investment that we may only ever do once. I agree that the accuracy and completeness of the drawing will be VERY important.

Thank you all for your suggestions and assistance. I'll let you know how this project turns out, though it may have to wait until next fiscal year, depending on costs. Better to get started now though.


Thanks!
SceneryDriver

 

[mcgyvr]

Whats wrong with off-the-shelf barbed t-nuts inserted from the bottom of the stage deck and regular bolts/screws? Drill a hole...hammer in insert from the back..screw in a bolt and call it a day..

They also make regular knife-thread inserts (in brass or stainless) for wood with standard US/Metric inner threads.. I don't see any reason to buy these "stage screws" and then cut off the hoop to make a regular screw when the same type of inserts without crazy acme threads are so readily available..

I see NO reason for a custom screw when there are TONS of other off the shelf solutions to try..

 

[TVP]

There are a number of standard insert products that you should be able to use with a spaced thread on the OD and a metric or inch thread on the ID. Then you can just purchase a standard Grade 5 bolt to mate with it. I agree with mcgyvr that a trapezoidal thread (ACME) is not needed for this application:

E-Z LOK

http://www.catalogds.com/db/service?domain=ezlok&command=browse&category=knife_thread

Yardley Products

http://www.yardleyproducts.com/products.php#selftapping

Grainger catalog

http://www.grainger.com/Grainger/kn.../ecatalog/N-8o0?Ndr=basedimid10071&sst=subset

 

[mcgyvr]

Check out Mcmaster.com (Or MSCDirect.com).. Very wide selection.. All the fasteners you could ever want for a simple application like this with quick shipping/decent prices..

 

[1gibson]

If you genuinely feel there is a need for a new design, others may feel the same way. Buy a bunch (min qty, or first price break above min qty) and start the marketing campaign so you can sell the extras. Take reasonable precautions to protect your design.

 

[tomwalz]

Try Tacoma Screw Products.

Sell a huge variety and custom manufacture.

Tom

P.S. Your pic was too big to open.

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[MikeHalloran]

I agree wih mcgyvr that a Tee-Nut is preferable for the internal threads, provided you have access to the far side of the panel.

I also agree that a generic screw is preferable for the male part.

But I disagree about the internal hex or internal Torx wrenching.
Both are subject to fouling from sand/ dirt/ debris/ floor wax. They work great in a clean factory environment, but in a floor, not so much. They are a really bad choice for, e.g. a dirt bike, where they are sold into the aftermarket because they look cool, to anyone who hasn't had to remove them after use.

A Phillips recess is still wrenchable with a little bit of dirt in it, and doesn't take magnification and an ice pick to get all the dirt out so you can engage a wrench.






Mike Halloran
Pembroke Pines, FL, USA

 

[77JQX]

How about Quiver Killers? They're meant for skis, but they're wood screw threads on the outside, machine threads on the inside.

 

[dinjin]

The thread in the picture with the square shown does not look like a 3/8 bolt thread. DSCN1940.JPG
I assume the other part is a keensert and probably a heavy duty one for wood applications. There must be a lot of keensert manufacturer that make steel keenserts. 3/8 looks more like the od of the keensert. I too see no advantage of having acme threads and would think a coarse 3/8-16 UUC pitch thread would be sufficient for you application rather than a 3/8-14 acme thread. If you want to use a stronger bolt you would have to increase the thickness of the head as it may limit the holding power of a stronger thread.

 

[chicopee]

I am a great believer in the Crosby product line. I would check out their on-line catalog for suitable machinery eyebolts with standard threads. Their products are reliable, safe if used as intended with high factor of safety, and American made. The drawbacks are that they do not publish threaded inserts and their prices is higher than Asian equivalent products which are of inferior quality.

 

[SceneryDriver]

To answer a few questions:
T-nuts are usually not an option, either because we can't get to the back/underside of where we need an insert. Further, the T-nuts tend to fall out or spin in their holes after a few assembly-disassembly reps.

We've tried regular (UNC thread) inserts and fasteners in the past, but with the number of repetitions that these fasteners see, we got an unacceptably high number of cross threading and/or galling incidents. That's why we went to the acme threaded inserts. The use of an acme thread is pretty standard in the scenery world, simply because the threads are so much more tolerant of abuse. The consensus from our stagehands is that flathead is actually preferred, so we will look into that style head instead of hex or Torx. I've found several companies on the web, along with those mentioned here, and we'll into contacting them.

Thanks for all the help and advice! This forum is wonderfully helpful and informative.


-SceneryDriver